When Is It Too Late To Spray For Weeds? – Spraying Guideline

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Looking at the bountiful, glossy lawn is incredibly satisfying until you spot some unwelcome guests. One of the most important external factors that can harm your plant species are pesky weeds. The backbone of weed control is, hands down, weed killers, be it postemergence herbicides or preemergence herbicides .

But then, when is it too late to spray for weeds? When is the perfect time to do so? As one of the external conditions, timing plays an important role in determining whether your effort works well. Let’s learn how to take advantage of the environment and get rid of those “guests”!

When Is It Too Late To Spray For Weeds?

This section will teach you which season will make your work useless and the perfect timing to get the annual lawn weeds under control.

How early can you spray for weeds

When Is It Too Late?

You shouldn’t carry out the job from late November onwards, as it’s the beginning of the winter season. The weather and atmosphere then get humid and cold, and those chemicals won’t work under such conditions. They will freeze overnight and what’s left is a waste of fortune!

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When Is The Best Time To Spray For Weeds?

How early can you spray for weeds? The earliest and most effective period is spring. Still, as we have mentioned, you just need to avoid the cold weather and frosting season of winter, then all the remaining seasons should be good to go. All in all, the ideal time to apply post-emergent weed killers should be spring and fall.

Spring is the beginning of many plants’ growing processes. Applications on time in the first place is always best. This season is also when the temperature and atmosphere are best for the herbicides to work. For pre-emergent weed killers, early spring is the golden chance to eliminate weed seeds, suitable for summer weeds preventative treatments.

If you miss spring, fall is your option number two. At this time, the unwanted plants haven’t gone strong yet. They are still vulnerable and weak for you to destroy them. Though summers are not as ideal as the two mentioned above, you can still affect the entire lawn.

Is it too late to spray for weeds in winter? Yes, it is. Yet, it doesn’t mean that there’s no point doing so. The temperature in different nations and days during winter may be slightly different, so we’ll break the information down into precise temperatures.

The OSU (Ohio State University) and the ISU (Iowa State University) have conducted research and found out that we can still kill multiple biennial weeds and perennial weeds effectively after several hard frosts in late winter. But that doesn’t mean you should apply your herbicide product right after the frost has gone.

How early can you spray for weeds

So, what is the best time of day to spray weeds during winter? The best way to carry out this job are as follow:

  • Daytime: above 50 degrees Fahrenheit
  • Nighttime: 40 degrees Fahrenheit

Besides, different types of weeds will react in their own ways when facing frost or cold seasons. Some plant species will still get protection from soil’s heat and can tolerate frost better than others. That’s why doing some inspection on their characteristics beforehand is extremely crucial.

Take an example of the grassy weeds of quackgrass. Effective control of weed growth with more than 8 inches high is to use glyphosate to control the plant below the ground and above parts. If they suffer 4 hours at 28 degrees Fahrenheit at night, they may die, so you don’t have to apply herbicide then.

However, they may regrow if, in the several following days, the warm temperatures reach at least 65 degrees Fahrenheit. Then, you might want to start your job immediately.

We will discuss this matter in-depth in the final section of this article.

How early can you spray for weeds

Why Does Time Matter?

Aren’t fertilizers, good soil, and herbicide application enough? Why is the actual time for applying that matter? The reasons stem from many aspects. Mostly because prevention is always better than cure and because different conditions of each season affect how the chemicals perform.

First and foremost, it’s always better to build up a defense against weeds before they destroy your green lawn. That’s why spring applications, when those species haven’t sprouted yet, are the most effective, costing you less in the long run.

Wet and warmer conditions can boost the effectiveness of weed killer. Only then can it penetrate the ground. The spring rain will help it do just that. If there is no rain, it will sit upon the surface and can do no good deeds.

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The frost of winter annuals will lower the soil temperatures, leading to the herbicide’s failure to penetrate the soil.

Fall is also an effective time, just less ideal than spring. It’s because during fall, those unwanted species are vulnerable. They have just faced the harsh changing conditions. By spraying them, you’re pushing them to die.

There is also an exception of weed killers that won’t penetrate into the soil and sit on the surface, foams. This type can be considered a herbicide for winter, is super convenient to use in any season, and won’t be affected by moisture.

what is the best time of day to spray weeds

What Are The Best Conditions To Apply Weed Killer?

Besides different seasons, you must also be aware of certain conditions.

Indeed, moisture is important, but moist doesn’t mean wet. If it’s about to rain, don’t apply it. Rainwater will dilute your herbicide and lessen its potency. You should apply if there is no rain in the next six hours.

What about the wind? It will also affect your weed killer. Wind will spread your weed killer out to many areas, which is not good for your plants. We recommend you do the job during mild weather. The conditions will not be too cold or hot (similar to spring conditions).

Hot weather makes it hard for the chemicals to enter the soil, lowering the herbicide’s movement. So, the rule of thumb here is to avoid freezing temperatures, frost, sunshine and look for mild and calm weather. Also, don’t forget to check out the product label for proper instructions.

Does The Type Of Weed Determine The Timing For Herbicides?

what is the best time of year to use weed killer

We have mentioned that types of weeds do affect how your herbicide will work. The secret lies in their life cycles.

Multiple types of pesky weeds come along many life cycles. The different life cycles indicate the changing of their sprouting time and many other issues. You will have to master this information to know the best application timing to target them.

Therefore, if you’re asking, what is the best time of year to use weed killer, the answer will depend on the specific weed you are targeting. You will need to know the weed’s annual life cycle to ensure you target it at its most vulnerable state.


So, when is it too late to spray for weeds? In general, late November must be the latest period. Yet you should look for specific weather conditions and weed types to grasp it to the fullest. Sometimes, doing it in the winter can still be effective defense against weeds due to some specific types and conditions.

Nevertheless, try to avoid application after November, especially when you want to treat a large spectrum of weeds. Never ignore the pesticide label, as it tells you when is the best time for each product (sometimes).

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